TRANSCRIPT ANALYSIS OF THE TOBACCO PLASTID OPERON RPS2 ATPI/H/F/A REVEALS THE EXISTENCE OF A NONCONSENSUS TYPE-II (NCII) PROMOTER UPSTREAM OF THE ATPI CODING SEQUENCE/

The plastid ATP synthase complex is composed of nine subunits, of whic h six are encoded in the plastome. The plastid-encoded genes are arran ged in two transcriptional units: atpB/E and atpI/H/F/A. We have recen tly reported that besides containing four -10 and -35 consensus-type ( CT) promoters, the atpB/E operon also contains a non-consensus type (N CII) promoter that alone is responsible for its expression in non-phot osynthetic plastids. As the functionality of ATP synthase requires exp ression of all nine subunits, NCII promoter-driven transcription of th e atpI/H/F/A operon is to be expected in non-photosynthetic plastids. Therefore, a detailed transcriptional analysis of this operon was carr ied out using RNA samples from tobacco leaf, cultured cells (BY-2) and seedlings grown on streptomycin and spectinomycin; which contain chlo roplasts, translationally active non-photosynthetic plastids and trans lationally inactive plastids, respectively. We identified a total of t hree transcription initiation sites (TIS) and four transcript processi ng sites in the noncoding regions of this operon. Our results also dem onstrate that rps2 is co-transcribed with the atpI/H/F/A genes. One of the TIS (-208 atpI) is characterized by an NCII type promoter, while other two primary transcripts (-131 atpI and -384 atpH) initiate from CT promoters. In non-photosynthetic plastids the atpI/H/F/A-specific t ranscript pool seems to be solely contributed by initiation at the -20 8 atpI (NCII type) promoter, because transcripts from CT promoters do not accumulate in these plastid types.